Composition containing a cross-linkable matrix precursor and a poragen, and a porous matrix prepared therefrom

ABSTRACT

A suitable cross-linkable matrix precursor and a poragen can be treated to form a porous cross-linked matrix having a T g  of greater than 300° C. The porous matrix material has a lower dielectric constant than the corresponding non-porous matrix material, making the porous matrix material particularly attractive for a variety of electronic applications including integrated circuits, multichip modules, and flat panel display devices.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. patent application Ser. No.09/447,011 filed Nov. 22, 1999, which claims priority from ProvisionalApplication Ser. No. 60/109,710 filed on Nov. 24, 1998.

This invention was made with United States Government support underCooperative Agreement No. 70NANB8H4013 awarded by NIST. The UnitedStates Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

The present invention relates to a composition that contains across-linkable matrix precursor and a poragen, and a porous matrixprepared therefrom.

As semiconductor devices become smaller and smaller, and chip packingdensities increase correspondingly, undesirable capacitatance relateddelays and cross-talk between metal interconnects are more acutelymanifested. Since capacitance related delays and cross-talk relate tothe dielectric constant of the insulator, attention has focused on thecreation of ultra-low dielectric constant materials (that is, dielectricmaterials having dielectric constants of ≦2.0). Such efforts includecreating porous inorganic (for example, silicon dioxide) orthermoplastic polymeric (for example, polyimide) materials.

Silicon dioxide, which has been the dominant inter-level dielectricmaterial (ILD) for the past 40 years, can be made porous bywell-developed sol-gel techniques such as those disclosed in Proc. Mat.Res. Soc. 381, 261 (1995); Proc. Mat. Res. Soc. 443, 91 (1997); andProc. Mat. Res. Soc. 443, 99 (1997), which teachings are incorporatedherein by reference. Although the introduction of pores into silicondioxide causes a reduction of dielectric constant from 4.2 to less than2.0, the resultant porous material is significantly weakened. Thus,porous silicon dioxide is impractical as a low dielectric constantmaterial.

Porous thermoplastic polymers, particularly thermally stable polymerssuch as polyimides, have also been investigated for use as ultra-lowdielectric materials. See, for example, U.S. Pat. Nos. 5,895,263 and5,776,990. Although these porous thermoplastic materials can be made tohave acceptable dielectric constants, the pores tend to collapse duringsubsequent high temperature processing, thereby precluding the use ofthese materials for the applications of interest.

In view of the deficiencies in the art, it would be desirable to have anultra-low dielectric material that is stable to the severe processingconditions required in fabricating semiconductors.

SUMMARY OF THE INVENTION

The present invention addresses the problems of the prior art byproviding a composition comprising a) a hydrocarbon-containing matrixprecursor; and b) a poragen; wherein the matrix precursor is selected toform upon curing a cross-linked, hydrocarbon-containing material havinga T_(g) of greater than 300° C. The cross-linked hydrocarbon-containingmaterial preferably has a thermal stability of at least 400° C.

In a second embodiment, the present invention is a low dielectricconstant material comprising a porous cross-linkedhydrocarbon-containing matrix having a T_(g) of greater than 300° C. Thematerial is preferably in the form of a thin film on a substrate.

In a third embodiment, the present invention is a method of making aporous film on a substrate comprising:

-   -   coating on a substrate, a solution comprising a matrix precursor        which cures to form a matrix material having a T_(g) of at least        300° C., a poragen, and a solvent;    -   removing the solvent;    -   reacting the matrix precursor to form the matrix material; and    -   degrading the poragen to form pores in the matrix. The removing,        reacting, and degrading steps are performed by one or more        heating steps as will be more thoroughly described below.

In a fourth embodiment, the present invention is an integrated circuitarticle comprising an active substrate containing transistors and anelectrical interconnect structure containing patterned metal linesseparated, at least partially, by layers or regions of a porousdielectric material, wherein the dielectric material comprises across-linked hydrocarbon-containing matrix having a T_(g) of greaterthan 300° C.

The present invention solves a problem in the art by providing a lowdielectric constant, porous matrix material that is suitable as aninterlayer dielectric for microelectronics applications and stable toprocessing temperature of greater than 300° C.

Definitions

B-Staged—refers to a partially polymerized monomer, or a mixture ofmonomer and partially polymerized monomer. A b-staged product is usuallysynonymous with “prepolymer” or “oligomer.”

Cross-linkable—refers to a matrix precursor that is capable of beingirreversibly cured, to a material that cannot be reshaped or reformed.Cross-linking may be assisted by UV, microwave, x-ray, or e-beamirradiation. Often used interchangeably with “thermosettable” when thecross-linking is done thermally.

Matrix precursor—a monomer, prepolymer, or polymer, or mixtures thereofwhich upon curing forms a cross-linked Matrix material.

Monomer—a polymerizable compound or mixture of polymerizable compounds.

Functionality—refers to the number of groups in a monomer available forpolymerization. For example, a biscyclopentadienone and a bis-acetyleneeach have a functionality of 2, while the monomer1,1,1-tris(4-trifluorovinyloxyphenyl)ethane has a functionality of 3.

Hydrocarbon-containing—refers to a matrix or matrix precursor thatcontains carbon and hydrogen, but may contain other elements. The matrixor matrix precursor preferably contains not more than 50 weight percentsilicon, more preferably not more than 30 weight percent silicon, andmost preferably not more than 20 weight percent silicon.

Poragen—a solid, liquid, or gaseous material that is removable from apartially or fully cross-linked matrix to create pores or voids in asubsequently fully cured matrix, thereby lowering the effectivedielectric constant of the resin.

Thermal stability temperature—the maximum temperature, T, at which theweight loss of a sample maintained at that temperature in an inertenvironment is less than 1 percent per hour.

Matrix—a continuous phase surrounding dispersed regions of a distinctcomposition. In the final article, the matrix is a solid phasesurrounding dispersed voids or pores.

DETAILED DESCRIPTION OF THE INVENTION

The porous matrix of the present invention can be prepared from amixture of a poragen and a cross-linkable hydrocarbon-containing matrixprecursor. The poragen may be reactive, so that the poragen becomeschemically bonded into the polymer matrix, or it may be non-reactive.

Matrix Precursors

Suitable matrix precursors are those that form cross-linked resinshaving a T_(g) of greater than 300° C. and more preferably greater than350° C.

Preferably, the matrix precursors are further characterized in that theyexperience either no decrease or only relatively small decreases inmodulus during cure. If the material experiences large modulus dropsduring cure, especially if the low modulus occurs at temperatures nearthe degradation temperature of the poragen, pore collapse may occur.

One preferred class of matrix precursors include thermosettablebenzocyclobutenes (BCBs) or b-staged products thereof, such as thosedescribed in U.S. Pat. No. 4,540,763 and U.S. Pat. No. 4,812,588, whichteachings are incorporated herein by reference. A particularly preferredBCB is1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethynyl)-1,1,3,3-tetramethyldisiloxane(referred to as DVS-bisBCB), the b-staged resin of which is commerciallyavailable as CYCLOTENE™ resin (from The Dow Chemical Company).

Another second preferred class of matrix materials include polyarylenes.Polyarylene, as used herein, includes compounds that have backbones madefrom repeating arylene units and compounds that have arylene unitstogether with other linking units in the backbone, e.g. oxygen in apolyarylene ether. Examples of commercially available polyarylenecompositions include SiLK™ Semiconductor Dielectric (from The DowChemical Company), Flare™ dielectric (from Allied Signal, Inc.), andVelox™ (Poly(arylene ether)) (from AirProducts/Shumacher). A preferredclass of polyarylene matrix precursor is a thermosettable mixture orb-staged product of a polycyclopentadienone and a polyacetylene, such asthose described in WO 98/11149, which teachings are incorporated hereinby reference. Examples of the thermosetting compositions orcross-linkable polyarylenes that may be used in the composition of thisinvention include monomers such as aromatic compounds substituted withethynylic groups ortho to one another on the aromatic ring as shown inWO 97/10193, incorporated herein by reference; cyclopentadienonefunctional compounds combined with aromatic acetylene compounds as shownin WO 98/11149, incorporated herein by reference; and the polyaryleneethers of U.S. Pat. Nos. 5,115,082; 5,155,175; 5,179,188 and 5,874,516and in PCT WO 91/09081; WO 97/01593 and EP 0755957-81, all of which areincorporated herein by reference. More preferably, the thermosettingcompositions comprise the partially polymerized reaction products (i.e.,b-staged oligomers) of the monomers mentioned above (see e.g., WO98/11149, WO 97/10193).

Preferably, the polyarylene precursors are characterized by a modulusprofile as measured by torsional impregnated cloth analysis (TICA)characterized in that during heating of the composition a MinimumMeasured Modulus observed in the temperature range from 300° C. to 400°C. occurs at a temperature T_(min), and said Minimum Measured Modulus isgreater than a value equal to 20 percent, more preferably 50 percent, ofa Measured Cured Modulus of the composition after heating to a maximumtemperature and cooling back down to T_(min). “Measured Heat-up Modulus”is the modulus at a given temperature detected for the test compositeduring the heating phase of the test on a plot of modulus versustemperature. “Minimum Measured Heat-up Modulus” is the minimum MeasuredHeat-up Modulus occurring in the temperature range of 300 to 450° C.“Measured Cured Modulus” is the modulus at a given temperature for thetest composite during the cool down phase. In this TICA technique, awoven glass cloth (preferably, 0.3 mm thick, 15 mm wide, and 35 mm longe.g., TA Instruments part number 980228.902) is mounted in a dynamicmechanical analyzer, such as a DuPont 983 DMA, preferably fitted with aLow Mass Vertical Clamp Accessory or equivalent functionality to enhancesensitivity. The ends of the cloth are wrapped in aluminum foil leaving10 mm in length exposed. The cloth is then mounted in the verticalclamps of the dynamic mechanical analyzer which are set 10 mm apart. Theclamps are tightened to about 12 inch pounds using a torque wrench. Thecloth is impregnated using a solution comprising the precursor compoundsat 10 to 30 percent solids via a pipet. The cloth is thoroughly soakedwith the solution and any excess is removed using the pipet. A heatdeflector and oven are attached and a nitrogen flow of about 3 standardcubic feet per hour is established. Amplitude of the displacement is setto 1.00 mm and frequency to 1 Hz. The sample is heated to 500° C. at 5°C. per minute and then allowed to cool. Data is collected during boththe heating and cooling stages. Data analysis may be performed to obtaintemperature versus flexural modulus values for the composite of glassand formulation. Prepared software programs such as DMA Standard DataAnalysis Version 4.2 from DuPont or Universal Analysis for Windows95/98/NT Version 2.5H from TA Instruments, may be used to perform thedata analysis. The modulus values themselves are not absolute values forthe tested formulation due to the contribution of the glass cloth andthe unavoidable variation in sample loading. However, using ratios ofthe modulus value at a point during heating to a modulus of thecomposite after cure and cool down to some consistent temperature givesa value, which can be used to compare different formulations. See alsorelated U.S. Pat. No. 6,359,091.

Preferred polyarylene-type matrix precursors comprise the followingcompounds, or more preferably, a partially polymerized (b-staged)reaction product of the following compounds:

-   -   (a) a biscyclopentadienone of the formula:    -   (b) a polyfunctional acetylene of the formula:        (c) and, optionally, a diacetylene of the formula:        R²≡Ar²≡R²    -   wherein R and R² are independently H or an unsubstituted or        inertly-substituted aromatic moiety and Ar¹, Ar² and Ar³ are        independently an unsubstituted aromatic moiety, or        inertly-substituted aromatic moiety, and y is an integer of        three or more. Stated alternatively, the most preferred matrix        precursor material comprises a curable polymer of the formula:        [A]_(w)[B]_(z)[EG]_(v)    -   wherein A has the structure:    -   and B has the structure:    -   end groups EG are independently represented by any one of the        formulas:        wherein R¹ and R² are independently H or an unsubstituted or        inertly-substituted aromatic moiety and Ar¹, Ar² and Ar³ are        independently an unsubstituted aromatic moiety or        inertly-substituted aromatic moiety and M is a bond, y is an        integer of three or more, p is the number of unreacted acetylene        groups in the given mer unit, r is one less than the number of        reacted acetylene groups in the given mer unit and p+r=y−1, z is        an integer from 1 to about 1000; w is an integer from 0 to about        1000 and v is an integer of two or more.

When the matrix precursor comprises a thermosettable mixture or b-stagedproduct of a polycyclopentadienone and a polyacetylene, the precursorspreferably are characterized so that branching occurs relatively earlyduring the curing process. Formation of a branched matrix early on inthe cure process minimizes the modulus drop of the matrix, and helpsminimize possible pore collapse, during the cure process, and/or allowsfor use of poragens that decompose or degrade at lower temperatures. Oneapproach for achieving this is to use a ratio of cyclopentadienonefunctionality to acetylene functionality in the precursor composition ofgreater than about 3:4, and preferably less than about 2:1, morepreferably about 1:1. A matrix precursor comprised of 3 parts3,3′-(oxydi-1,4-phenylene)bis(2,4,5-triphenycyclpentadienone) and 2parts 1,3,5-tris(phenylethynyl)benzene (molar ratios) is an example ofsuch a system. Alternatively, additional reagents capable ofcross-linking the thermosettable mixture or b-staged product of apolycyclopentadienone and a polyacetylene can be added to minimize themodulus drop of the matrix during the cure process. Examples of suitablereagents include bisorthodiacetylenes as disclosed, for example, in WO97/10193, incorporated herein by reference; monoorthodiacetylenes;bistriazenes; tetrazines, such as 1,3-diphenyltetrazine; bisazides, suchas bissulfonylazides; and peroxides, including diperoxides. The loadinglevels of the reagent can vary from <1 weight percent based on solidsto >30 weight percent based on solids.

A third example of a matrix precursor suitable for the preparation ofthe porous matrix of the present invention is a thermosettableperfluoroethylene monomer (having a functionality of 3 or more) or ab-staged product thereof, the disclosure and preparation of which can befound in U.S. Pat. No. 5,023,380 (col. 4, starting on line 38), and U.S.Pat. No. 5,540,997 (col. 3, lines 4 to 46), which teachings areincorporated herein by reference. A preferred thermosettableperfluoroethylene is 1,1,1-tris(4-trifluorovinyloxyphenyl)ethane. Thethermosettable perfluoroethylene monomer may also be convenientlycopolymerized with a perfluoroethylene monomer having a functionality oftwo, prepared as described in U.S. Pat. Nos. 5,021,602; 5,037,917; and5,246,782. Another polyarylene matrix precursor is a thermosettablebis-o-diacetylene or b-staged product thereof as described in WO97/10193, which teachings are incorporated herein by reference.According to this embodiment the precursor comprises a compound of theformula(R—C≡C—[Ar—L+Ar—C≡C—R)_(m)]_(q)wherein each Ar is an aromatic group or inertly-substituted aromaticgroup and each Ar comprises at least one aromatic ring; each R isindependently hydrogen, an alkyl, aryl or inertly-substituted alkyl oraryl group; L is a covalent bond or a group which links one Ar to atleast one other Ar; preferably a substituted or unsubstituted alkylgroup, n and m are integers of at least 2; and q is an integer of atleast 1, and wherein at least two of the ethynylic groups on one of thearomatic rings are ortho to one another.Poragens and Methods of Forming Porous Cross-Linked Dielectrics

The poragen materials are materials that will form domains (or discreteregions) in the matrix or matrix precursor. Preferably, the domainsshould be no larger than the final desired pore size.

Many polymeric materials may be useful as poragens. However, a poragenthat functions well with a first matrix system will not necessarilyfunction well with another matrix system. The compatibility poragen withthe matrix system must be high enough that very large domains are notformed but cannot be so high that no domains are formed.

The poragens useful in this invention are preferably those thatthermally degrade (i.e., burnout) at temperatures below the thermalstability temperature of the matrix material. The degradationtemperature range may overlap with the curing temperature range so longas curing occurs more quickly than (or before) degradation allowing thematrix to set before the poragen is substantially removed. Thesematerials preferably decompose primarily into low molecular weightspecies and, thus, do not leave substantial “char” in the porous matrix.

Examples of poragens and methods by which they can be used inconjunction with the matrix precursor to form porous cross-linked matrixmaterials are described as follows.

The poragen may be a block copolymer (e.g., a di-block polymer). Suchmaterials may be capable of self-assembling, as described in PhysicsToday, February 1999, p. 32, if the blocks are immiscible to giveseparated domains in the nanometer size range. Such a block copolymercan be added to the cross-linkable matrix precursor with or withoutsolvent to obtain a formulation suitable for processing. The blockcopolymer can self-assemble during processing (e.g., after spin coating,but before the matrix is formed). One or more of the blocks may bereactive with the matrix or the blocks may be non-reactive. One or moreof the blocks may be compatible with the matrix, or its precursor, butpreferably at least one block is incompatible with the matrix. Usefulpolymer blocks can include an oligomer of the matrix precursor,polyvinyl aromatics, such as polystyrenes, polyvinylpyridines,hydrogenated polyvinyl aromatics, polyacrylonitriles, polyalkyleneoxides, such as polyethylene oxides and polypropylene oxides,polyethylenes, polylactic acids, polysiloxanes, polycaprolactones,polycaprolactams, polyurethanes, polymethacrylates, such aspolymethylmethacrylate or polymethacrylic acid, polyacrylates, such aspolymethylacrylate and polyacrylic acid, polydienes such aspolybutadienes and polyisoprenes, polyvinyl chlorides, polyacetals, andamine-capped alkylene oxides (commercially available as Jeffamine™polyether amines from Huntsman Corp.) For example, a diblock polymerbased on polystyrene and polymethylmethacrylate can be added to asolution of CYCLOTENE™ resin in a suitable solvent such as mesitylene ata weight:weight ratio of resin to diblock polymer of preferably not lessthan about 1:1, and more preferably not less than 2:1, and mostpreferably not less than 3:1. The overall solids content is applicationdependent, but is preferably not less than about 1, more preferably notless than about 5, and most preferably not less than about 10 weightpercent, and preferably not greater than about 70, more preferably notgreater than about 50, and most preferably not greater than 30 weightpercent. The solution can then be spin-coated onto a silicon waferleaving a thin film containing a dispersed phase of diblock copolymer ina continuous phase of DVS-bisBCB. The film can then be thermally curedleaving a crosslinked polymer system containing a dispersed phase ofpoly(styrene-b-methylmethacrylate) in a continuous phase of cross-linkedDVS-bisBCB. The diblock copolymer can then be decomposed or removed toleave a porous cross-linked DVS-bisBCB polymer. Similarly, a diblockpolymer based on polystyrene and polybutadiene can be added to ab-staged solution of a dicyclopentadienone (e.g.,3,3′-(oxydi-1,4-phenylene)bis(2,4,5-triphenycyclpentadienone)) and atrisacetylene (e.g., 1,3,5-tris(phenylethynyl)benzene).

Thermoplastic homopolymers and random (as opposed to block) copolymersmay also be utilized as poragens. As used herein, “homopolymer” meanscompounds comprising repeating units from a single monomer. Suitablethermoplastic materials include polystyrenes, polyacrylates,polymethacrylates, polybutadienes, polyisoprenes, polyphenylene oxides,polypropylene oxides, polyethylene oxides, poly(dimethylsiloxanes),polytetrahydrofurans, polyethylenes, polycyclohexylethylenes,polyethyloxazolines, polyvinylpyridines, polycaprolactones, polylacticacids, copolymers of these materials and mixtures of these materials.The thermoplastic materials may be linear, branched, hyperbranched,dendritic, or star like in nature.

Polystyrene has been found to be particularly suitable withthermosettable mixtures or b-staged products of a polycyclopentadienoneand a polyacetylene, such as those described in WO 98/11149, because itdecomposes at a high temperature (e.g., around 420° C. to 450° C.) andalso decomposes primarily into the monomer which can then diffuse out ofthe matrix. Any known polystyrene may be useful as the porogen. Forexample, anionic polymerized polystyrene, syndiotactic polystyrene,unsubstituted and substituted polystyrenes (e.g., poly(a-methylstyrene)) may all be used as the poragen. Unsubstituted polystyrene isespecially preferred.

For example, an anionically polymerized polystyrene with a numberaverage molecular weight of 8,500 can be blended with a polyaryleneb-staged reaction product of a polycyclopentadienone and apolyacetylene. This solution can then be spin-coated onto a siliconwafer to create a thin film containing the dispersed phase ofpolystyrene in the polyarylene matrix precursor. The coated wafer iscured on a hot plate to form the matrix, then the polystyrene poragen isremoved by thermal treatment in an oven to form a porous polyarylenematrix.

The poragen may also be designed to react with the cross-linkable matrixprecursor during or subsequent to b-staging to form blocks or pendantsubstitution of the polymer chain. Thus, thermoplastic polymerscontaining, for example, reactive groups such as vinyl, acrylate,methacrylate, allyl, vinyl ether, maleimido, styryl, acetylene, nitrile,furan, cyclopentadienone, perfluoroethylene, BCB, pyrone, propiolate, orortho-diacetylene groups can form chemical bonds with the cross-linkablematrix precursor, and then the thermoplastic can be removed to leavepores. The thermoplastic polymer can be homopolymers or copolymers ofpolystyrenes, polyacryclates, polymethacrylates, polybutadienes,polyisoprenes, polyphenylene oxides, polypropylene oxides, polyethyleneoxides, poly(dimethylsiloxanes), polytetrahydrofurans, polyethylenes,polycyclohexylethylenes, polyethyloxazolines, polycaprolactones,polylactic acids, and polyvinylpyridines or mixtures thereof. A singlereactive group or multiple reactive groups may be present on thethermoplastic. The number and type of reactive group will determinewhether the thermoplastic poragen is incorporated into the matrix as apendant material or as a block. The thermoplastic materials may belinear, branched, hyperbranched, dendritic, or star like in nature.

For example, a low molecular weight (<10,000 M_(n)) polypropylene glycololigomer can be end-capped with cinnamate groups, then added at about 10to about 30 weight percent to a neat DVS-bisBCB monomer. This mixturecan then be b-staged by heating, then diluted with a suitable solventsuch as mesitylene and spin-coated onto a silicon wafer to create a thinfilm containing a dispersed phase of polypropylene glycol oligomerschemically bonded to the b-staged DVS-bisBCB. The dispersedpolypropylene glycol oligomers can then be decomposed to leave a porouscross-linked DVS-bisBCB polymer.

The desired molecular weight of polymeric poragens will vary with avariety of factors, such as their compatibility with the matrixprecursor and cured matrix, the desired pore size, etc. Generally,however, the number average molecular weight of the poragen is greaterthan about 2000 and less than about 100,000. More preferably themolecular weight is in the range of about 5000 to about 50,000 and mostpreferably less than about 35,000. The poragen polymer also preferablyhas a narrow molecular weight distribution.

The poragen may also be a material that has an average diameter of about1 to about 50 nm. Examples of such materials include dendrimers(polyamidoamine (PAMAM), dendrimers are available through Dendritech,Inc., and described by Tomalia, et al., Polymer J. (Tokyo), Vol. 17, 117(1985), which teachings are incorporated herein by reference;polypropylenimine polyamine (DAB-Am) dendrimers available from DSMCorporation; Frechet type polyethereal dendrimers (described by Frechet,et al., J. Am. Chem. Soc., Vol. 112, 7638 (1990), Vol. 113, 4252(1991));Percec type liquid crystal monodendrons, dendronized polymers and theirself-assembled macromolecules (described by Percec, et al., Nature, Vol.391, 161(1998), J. Am. Chem. Soc., Vol. 119, 1539(1997)); hyperbranchedpolymer systems such as Boltron H series dendritic polyesters(commercially available from Perstorp AB) and latex particles,especially cross-linked polystyrene containing latexes. These materialsmay be non-reactive with the cross-linkable matrix precursor, orreactive as described above. For example, a generation 2 PAMAM(polyamidoamine) dendrimer from Dendritech, Inc. can be functionalizedwith vinyl benzyl chloride to convert amine groups on the surface of thedendrimer to vinyl benzyl groups. This functionalized dendrimer can thenbe added to a solution of b-staged DVS-bisBCB in mesitylene, and themixture can then be spin-coated on a silicon wafer to obtain a dispersedphase of PAMAM dendrimer in DVS-bisBCB oligomers. The film can bethermally cured to obtain a cross-linked polymer system containing adispersed phase of PAMAM dendrimer chemically bonded to a continuousphase of cross-linked DVS-bisBCB. The dendrimer can then be thermallydecomposed to obtain the porous cross-linked DVS-bisBCB polymer.Alternatively, a generation 4 Boltron dendritic polymer (H40) fromPerstorp AB can be modified at its periphery with benzoyl chloride toconvert hydroxy groups on the surface of the dendrimer to phenyl estergroups. This functionalized dendrimer can then be added to a precursorsolution of partially polymerized (i.e., b-staged) reaction product of apolycyclopentadiene compound and a polyacetylene compound in a solventmixture of gamma-butyrolactone and cyclohexanone. The mixture can thenbe spin-coated on a silicon wafer to obtain a dispersed phase of BoltronH40 benzoate dendritic polymers in precursor oligomers. The film can bethermally cured to obtain a cross-linked polymer system containing adispersed phase of dendrimer chemically bonded to a continuous phase ofcross-linked polyarylene. The dendrimer can then be thermally decomposedat 400° C. to obtain the porous cross-linked polyarylene.

Alternatively, the poragen may also be a solvent. For example, ab-staged prepolymer or partially cross-linked polymer can first beswollen in the presence of a suitable solvent or a gas. The swollenmaterial can then be further cross-linked to increase structuralintegrity, whereupon the solvent or gas can be removed by applyingvacuum or heat. Suitable solvents would include mesitylene, pyridine,triethylamine, N-methylpyrrolidinone (NMP), methyl benzoate, ethylbenzoate, butyl benzoate, cyclopentanone, cyclohexanone, cycloheptanone,cyclooctanone, cyclohexylpyrrolidinone, and ethers or hydroxy etherssuch as dibenzylethers, diglyme, triglyme, diethylene glycol ethylether, diethylene glycol methyl ether, dipropylene glycol methyl ether,dipropylene glycol dimethyl ether, propylene glycol phenyl ether,propylene glycol methyl ether, tripropylene glycol methyl ether,toluene, xylene, benzene, dipropylene glycol monomethyl ether acetate,dichlorobenzene, propylene carbonate, naphthalene, diphenyl ether,butyrolactone, dimethylacetamide, dimethylformamide and mixturesthereof. The concentration of pores in the porous matrix is sufficientlyhigh to lower the dielectric constant of the matrix but sufficiently lowto allow the matrix to withstand the process steps required in themanufacture of the desired microelectronic device (for example, anintegrated circuit, a multichip module, or a flat panel display device).Preferably, the density of pores is sufficient to lower the dielectricconstant of the matrix to less than 2.5, more preferably to less than2.0. Preferably, the concentration of the pores is at least 5 volumepercent, more preferably at least 10 volume percent and most preferablyat least 20 volume percent, and preferably not more than 70 volumepercent, more preferably not more than 60 volume percent based on thetotal volume of the porous matrix.

The average diameter of the pores is preferably less than about 400 nm;more preferably, less than 100 nm; more preferably still, not more thanabout 50 nm; even more preferably, not more than about 20 nm; and mostpreferably, not more than about 10 nm.

Methods of Preparing a Porous Matrix Layer

While not being bound by theory, it is thought that the following eventsoccur during the processing of solutions containing a matrix precursorand a poragen. The solution of matrix precursor and poragen is appliedto a substrate by a method such as spin coating. During this applicationsome of the solvent evaporates leaving a more concentrated solution onthe substrate. The coated substrate is then heated on a hot plate toremove most of the remaining solvent(s) leaving the poragen dispersed inthe matrix precursor. During the solvent removal process and/or duringsubsequent thermal processing, the poragen phase separates from thematrix precursor. This phase separation may be driven by loss of solvent(concentration effect and/or change in solubility parameter of thesolution), increases in molecular weight of the matrix precursor,assembly or aggregation of sufficient poragen mass in a specificlocation, or combinations thereof. With further heat treatments, thematrix becomes more fully cured. At an elevated temperature the poragenbegins to decompose into fragments which can diffuse out of the coatedfilm leaving behind a pore, thus forming a porous matrix.

The matrix precursor, the poragen and a solvent are combined and mixedto form an optically clear solution. The amount of matrix precursorrelative to the amount of poragen may be adjusted to give the desiredporosity. However, preferably, the weight percent of poragen based onweight of poragen and matrix is at least 5 percent, more preferably atleast 10 percent, and most preferably at least 20 percent. The maximumamount of poragen will be determined by the mechanical and electricalproperties desired in the final product. Preferably, the weight percentporagen is no greater than 80 percent, more preferably no greater than70 percent, and most preferably no greater than 60 percent.

Sufficient solvent to provide an optically clear solution should beused. In addition, the amount of solvent may be varied to allow one toget various coating thicknesses. The more solvent that is used, thethinner the layer of the final film. Preferably, the amount of solventis in the range of 50-95 percent by weight of the total solution.

Any known coating method may be used to apply theprecursor/poragen/solvent composition to a substrate. Spin coating isparticularly suitable for providing the very thin film layers desired.Preferred film thicknesses are less than about 10 microns, preferablyless than about 5 microns, for interlevel dielectric films. Thecomposition may be applied to any substrate where a thin porous film isdesired. Preferably, the substrate comprises a silicon wafer. Thesubstrate may further comprise other layers or features such as arefound in integrated circuits (e.g., gates, metal interconnect lines,other insulating materials, etc.).

The solvents used may be any solvent or combination of solvents in whichthe combination of poragen and matrix precursor forms a solution.Examples of suitable solvents include mesitylene, pyridine,triethylamine, N-methylpyrrolidinone (NMP), methyl benzoate, ethylbenzoate, butyl benzoate, cyclopentanone, cyclohexanone, cycloheptanone,cyclooctanone, cyclohexylpyrrolidinone, and ethers or hydroxy etherssuch as dibenzylethers, diglyme, triglyme, diethylene glycol ethylether, diethylene glycol methyl ether, dipropylene glycol methyl ether,dipropylene glycol dimethyl ether, propylene glycol phenyl ether,propylene glycol methyl ether, tripropylene glycol methyl ether,toluene, xylene, benzene, dipropylene glycol monomethyl ether acetate,dichlorobenzene, propylene carbonate, naphthalene, diphenyl ether,butyrolactone, dimethylacetamide, dimethylformamide and mixturesthereof.

The poragen and matrix precursor may be simply mixed prior toapplication or they may be partially reacted or b-staged prior toapplication of the solution to the desired substrate. The poragen may beadded at various stages of the matrix precursor B-staging process asdesired.

After the matrix precursor film is formed, the film can be baked underconditions sufficient to remove solvent and cause further polymerizationof the matrix precursor. Baking temperature is system dependent and canbe determined by one of ordinary skill in the art without undueexperimentation. The subsequently formed coating of matrix precursor ormatrix material, which is typically about 0.1 to about 5 microns thick,can be smoothed, if desired, by chemical mechanical polishing (CMP).Poragen can be removed either before or after the CMP process.

A thermal decomposition of the poragen to low molecular weight speciesthat do not leave substantial residue in the matrix is preferred. Afterapplying the composition to the substrate, the solvent is removed;typically, by heating to a moderate temperature. The composition is thenheated rapidly to at least a temperature sufficient to cross-link theprecursor materials and form the matrix. The poragen is removed byheating to a temperature sufficient to decompose the poragen. When apolystyrene containing poragen is used, it is preferred that the heatingoccurs in the absence of oxygen. While the drying (solvent removal),curing, and decomposition steps may occur by separate heating steps, itis also possible that a single heating step could be used and it isrecognized that even if multiple heating stages are used, more than oneof the processes may be occurring in any given heating step.

Preferably, at least 80 percent of the poragen is removed, morepreferably at least 90 percent, and most preferably at least 95 percent.Removal of the poragen may be determined by techniques such as infraredspectroscopy, transmission electron microscopy, etc. Removal of theporagen may occur when the poragen degrades into low molecular weightspecies that can diffuse from the film. Preferably, at least 80 percentof the poragen degrades into low molecular weight species, morepreferably at least 90 percent, and most preferably at least 95 percent.Preferably, at least 80 pecent, more preferably at least 90 percent andmost preferably at least 95 percent of the thermoplastic poragendegrades into its monomeric units or smaller units.

According to one preferred embodiment, after coating, the coatedsubstrate is heated to a temperature sufficient to cause rapid cure butbelow the decomposition temperature for the poragen. Suitable methodsfor performing such a rapid heating step include baking on a hot plate,and rapid thermal anneal under infrared lamps. For the preferred matrixmaterials, such as those found in WO 98/11149, the compositionpreferably is raised to a temperature of above about 300° C., morepreferably about 350° C., at a rate of at least 20° C. per second, morepreferably at least 50° C. per second. This initial curing step need notcause complete cure, so long as the matrix is sufficiently cured as to“lock” the structure of the poragen and the matrix. At least oneadditional heating step is then performed to fully complete the cure, ifnecessary, and to decompose the poragen. This subsequent heating steppreferably occurs at temperatures above about 400° C., more preferablyabove about 420° C., and preferably less than about 500° C., morepreferably less than 470° C.

According to an alternate embodiment, a single rapid heating step at arate of preferably at least 20° C. per second, more preferably at least50° C. per second, to a temperature sufficient to cause both cure anddecomposition of the poragen may be used. In this embodiment, eitherafter drying or without using a separate drying step, the temperature israpidly raised. For the preferred matrix materials, such as those foundin WO 98/11149, the temperature is raised to greater than 400° C., andmore preferably greater than 420° C.

If multiple layers of the film are desired, the above steps may berepeated. Also, after forming the porous film, that layer may be etchedor imaged by known methods to form trenches, vias, or holes, as aredesired in manufacture of an integrated circuit article and othermicroelectronic devices.

The cross-linked hydrocarbon-containing matrix/poragen system isselected such that the matrix forms before the poragen degrades, and theporagen degrades completely or substantially completely before thematrix degrades. It is preferable that the temperature window fromcross-linking to degradation of the matrix be wide to have the greatestflexibility in the choice of poragen.

Poragen can be removed by a number of methods including the preferredthermal burnout method discussed above. This thermal burnout may occurin the absence of oxygen or with oxygen present or even added toaccelerate the removal of poragen. This second approach is particularlydesirable where the thermosetting matrix is comparativelythermo-oxidatively stable. Poragen can also be removed by wetdissolution, wherein the poragen is effectively dissolved away from thethermoset with an appropriate solvent or by dry or plasma removal,wherein plasma chemistry is used to remove the poragen selectively. Forexample, a solvent or supercritical gas, such as those listed above, canbe used to dissolve and remove a dispersed second phase. The secondphase may be a thermoplastic material, a diblock polymer, an inorganicmaterial, or any material that can be dispersed on a nanoscale level andis capable of being dissolved in a solvent that can diffuse into and outof a polymer system.

The porous cross-linked matrix of the present invention may be used asone or more of the insulating or dielectric layers in single or multiplelayer electrical interconnection architectures for integrated circuits,multichip modules, or flat panel displays. The polymer of the inventionmay be used as the sole dielectric in these applications, or inconjunction with inorganic dielectrics such as silicon dioxide, siliconnitride, or silicon oxynitride, or with other organic polymers.

The porous hydrocarbon-containing matrix material of the presentinvention is particularly useful as a low dielectric constant insulatingmaterial in the interconnect structure of an integrated circuit, such asthose fabricated with silicon or gallium arsenide. The poroushydrocarbon-containing matrix material may also be used in the processfor making integrated circuit devices as disclosed in U.S. Pat. Nos.5,550,405 and 5,591,677, which teachings are incorporated herein byreference.

The following examples are for illustrative purposes only and are notintended to limit the scope of this invention.

EXAMPLE 1 Preparation of a Porous Benzocyclobutene Matrix

Using a Reactive Thermoplastic Oligomer Preparation of Poly(propyleneglycol) Biscinnamate

Into a 250 mL round bottom flask equipped with a magnetic stirrer, anequilibrating addition funnel, and a reflux condenser with a nitrogeninlet was added, with stirring, poly(propylene glycol) having a numberaverage molecular weight of 8000 (38.21 g, 4.78 mmol) and chloroform (40mL). Pyridine (0.60 g, 7.64 mmol) was then added to the stirredsolution. Cinnamoyl chloride (0.64 g, 3.82 mmol) was added dropwise tothe solution over 15 minutes. Upon completion of addition, the reactionmixture was heated under reflux for 18 hours. The reaction was thencooled to room temperature. The solution was washed with 10 percent HCl(3×25 mL), then water (1×50 mL), then 1M NaOH (2×25 mL), then wateragain (1×50 mL), then brine (1×50 mL). The organics were then dried overmagnesium sulfate, and the solvent removed to yield the product (37.5 g)the structure of which was confirmed by proton and carbon NMRspectroscopy.

Preparation of a Copolymer Divinylsiloxane-bis-benzocyclobutene andPoly(propylene glycol) Biscinnamate

Into a glass reactor was placed divinylsiloxane-bis-benzocyclobutene(CAS# 124221-30-3) (4.0 g, 1.024×10⁻² mol) and poly(propylene glycol)biscinnamate (1.0 g, 1.22×10⁻⁴ mol). The mixture, which formed a singlephase, was heated at 200° C. for 18 hours, whereupon the material hadbecome white and hard. This material was heated to 325° C. undernitrogen for 50 hours to afford a porous article having a pore size (asdetermined by transmission electron microscopy) in the range of about 10to about 50 nm.

EXAMPLE 2 Preparation of a Porous Thin Film of a Benzocyclobutene

Matrix Using a Reactive Thermoplastic Oligomer

A solution of oligomeric divinylsiloxane-bisbenzocyclobutene, Mw 49600in mesitylene, 80 parts was combined with 20 parts of the poly(propyleneglycol) biscinnamate prepared from poly(propylene glycol) Mw 4000. Thissolution was heated at 165° C. under nitrogen for 4.5 hours to furtheradvance the molecular weight. Upon cooling to room temperature, thetotal percent solids of the solution was adjusted to 20 percent byaddition of the appropriate amount of mesitylene.

Ten milliliters of the above solution was puddled onto a 4 inch siliconwafer and first spun at 500 rpm for 3 seconds followed by spinning at2,000 rpm for 30 seconds. The wafer was then subjected to the followingthermal conditions: hot plate for 5 minutes at 200° C.; 250° C. for 6minutes; 350° C. for 10 minutes. The wafer was transferred to an ovenwith a nitrogen atmosphere and held at 300° C. for 9 hours. Transmissionelectron microscopy indicated the presence of pores which ranged in sizefrom 20-100 nm with an average value of 60-70 nm

EXAMPLE 3 Preparation of a Porous Polyarylene Thin Film Using a ReactivePolystyrene Poragen

Preparation of 3,5-Bis(phenylethynyl)benzoyl Chloride

-   -   a.) Preparation of Methyl 3,5-Dibromobenzoate

To a 250 mL round bottom flask fitted with a condenser and nitrogeninlet were added 3,5-dibromobenzoic acid (30.06 g, 0.1074 mole),methanol (60 g, 1.87 moles), and concentrated sulfuric acid (1.8 mL).The mixture was heated to reflux for 23 hours and the mixture was cooledto room temperature during which time a solid precipitated. The mixturewas cooled in an ice bath and the solid isolated by filtration. Thesolid was rinsed with cold methanol and then dried in vacuo at 40° C.Reaction and final product were analyzed by GC to monitor reactionprogress and assess purity of product.

-   -   b.) Coupling of Methyl 3,5-Dibromobenzoate with Phenylacetylene

To a 1 L round bottom flask fitted with a nitrogen inlet was addedmethyl 3,5-dibromobenzoate (26.4 g, 0.08981 mole), palladium chloridebis(triphenylphosphine) (6.258 g, 0.008916 mole), triphenylphosphine(1.18 g, 0.004504 mole), phenylacetylene (27.40 g, 0.2682 mole),triethylamine (36.13 g, 0.3569 mole), and tetrahydrofuran (THF) (500mL). The mixture was stirred at room temperature for 20 minutes.Copper(I) iodide (0.428 g, 0.00225 mole) was then added and the mixturestirred at room temperature for 95 hours. Reaction was followed by GC.Solvent was removed in vacuo. Residue was slurried with methanol andisolated by filtration. Solid was dissolved in methylene chloride andfiltered through a plug of silica gel in a filter funnel. Solvent wasremoved in vacuo to give a brown solid.

-   -   c.) Preparation of 3,5-Bis(phenylethynyl)benzoic Acid

To a 1 L round bottom flask was added methyl3,5-bis(phenylethynyl)benzoate (32.7 g, 0.0972 mole) and isopropanol(261 mL). The mixture was heated to reflux until all the soliddissolved. Potassium hydroxide (24.24 g of 45 percent KOH aq., 0.1944mole) was added and the mixture was kept hot for 4 hours. The mixturewas allowed to cool then acidified with concentrated HCl until solidprecipitated. The solid was isolated by filtration and dried in vacuo at80° C. overnight giving a grayish solid (about 22 g). The solid wasrefluxed in toluene with decolorizing charcoal, filtered hot throughfilter aid, and cooled during which time a solid precipitated. The solidwas isolated by filtration and dried in vacuo overnight. Analysis byhigh performance liquid chromatography (HPLC) showed the material to bepure. The material was further analyzed by ¹H-NMR and ¹³C-NMR. Spectrawere consistent with the desired structure.

d.) Preparation of 3,5-Bis(phenylethynyl)benzoyl Chloride

3,5-Bis(phenylethynyl)benzoic acid (2.7982 g, 0.008680 mole), oxalylchloride (2.2 mL, 0.02521 mole), and toluene (7 mL) were added to a 50mL round bottom flask. The mixture was heated at 50° C. until all thesolid had dissolved plus an additional hour. The solvent and excessoxalyl chloride were removed by applying a vacuum. The solid wasredissolved in toluene at room temperature then solvent removed byapplying vacuum. Solid was used subsequently without furtherpurification.

Preparation of a Poly(styrene) Ester of 3,5-Bis(phenylethynyl)benzoicAcid

Charged to a 1.5 L glass polymerization reactor, which had been cleanedwith refluxing toluene and dried under vacuum, was 700 mL of cyclohexane(passed through activated alumina). The reactor was heated to 55° C. and103.3 g of styrene (passed through activated alumina, distilled fromcalcium hydride and dibutylmagnesium prior to use) were added. Thepolymerization was initiated by adding 9.0 mL (3.456 mmoles) of 0.384 Msec-butyl lithium solution. After stirring for 1 hour, 0.60 g ofethylene oxide (dried over calcium hydride) was added causing the orangecolor solution to become colorless. After 30 minutes, 1.778 g (3.456mmoles, 1.0 equivalent) of 3,5-bis(phenylethynyl)benzoyl chloride, in 10mL of tetrahydrofuran (passed through activated alumina) were added.After 30 minutes, the solution was cooled and removed from the reactor.The polymer was isolated by precipitating it in 1.5 L of methanol anddrying it under vacuum at 80° C. overnight. The yield was quantitative.GPC analysis, versus narrow molecular weight polystyrene standards, ofthe polymer gave M_(n)=39,353, M_(w)=41,303 and M_(w)/M_(n)=11.050.Analogously, functionalized polystyrenes with M_(n) values of about46,500 and about 50,000 were also prepared.

Preparation of Oligomer Solution from4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether,1,3,5-Tris(phenylethynyl)benzene and Polystyrene Ester of3,5-Bis(phenylethynyl)benzoic Acid

To a 500 mL 3-necked round bottom flask was added4,4′-bis(2,4,5-triphenylcyclopentadienone)diphenyl ether (45.38 g,0.0580 mole), 1,3,5-tris(phenylethynyl)benzene (14.62 g, 0.0386 mole),polystyrene ester of 3,5-bis(phenylethynyl)benzoic acid (M_(n)=39,353)(15.00 g, 0.000375 mole), and gamma-butyrolactone (140 g). The flask wasattached to a nitrogen/vacuum inlet. The magnetically stirred solutionwas degassed by applying vacuum and refilling with nitrogen five times.The solution was then heated to an internal temperature of 200° C. After55.5 hours of heating, the solution was allowed to cool to 145° C. thendiluted with cyclohexanone (205 g). The solution was then allowed tocool to room temperature. Analysis of the final solution by gelpermeation chromatography indicated a M_(n)=5362 and a M_(w)34022relative to a polystyrene standard. Similar solutions using othermolecular weight reactive polystyrenes were prepared analogously.

Preparation and Evaluation of Porous Thin Film

A resin solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene containing the polystyrene ester of3,5-bis(phenylethynyl)benzoic acid (M_(n)=46,500) as the poragen wasprepared as described above. The solution was applied to a silicon waferand cast by spin-coating to form a 1.16 μm thick coating. The film wasbaked on an MTI hot plate at 320° C. for 2 minutes under nitrogen andthen at 400° C. for 10 minutes under nitrogen. The coating on the waferwas further heated at 450° C. under nitrogen for 20 minutes in a Blue Moven. The pores were about 120 nm in diameter based on visual inspectionof a TEM view of the film. The refractive index was 1.58.

EXAMPLE 4 Preparation of Porous Polyarylene Thin Films UsingNon-Reactive Polystyrene Poragens

Preparation of Oligomer Solution from4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl Ether and1,3,5-Tris(phenylethynyl)benzene Mole Ratio 3:2

To a 500 mL 3-necked round bottom flask was added4,4′-bis(2,4,5-triphenylcyclopentadienone)diphenyl ether (60.00 g,0.07662 mole), 1,3,5-tris(phenylethynyl)benzene (19.34 g, 0.0511 mole),and gamma-butyrolactone (185 g). The flask was attached to anitrogen/vacuum inlet. The magnetically stirred solution was degassed byapplying vacuum and refilling with nitrogen five times. The solution wasthen heated to an internal temperature of 200° C. After 48 hours ofheating, the solution was allowed to cool to 145° C. then diluted withcyclohexanone (132 g). The solution was then allowed to cool to roomtemperature. Analysis of the final solution by gel permeationchromatography indicated a M_(n)=5550 and a M_(w)=30550 relative to apolystyrene standard.

Preparation of Anionically Polymerized Polystyrene

Charged to a 1.5 L glass polymerization reactor, which had been cleanedwith refluxing cyclohexane and dried under vacuum, was 750 mL ofcyclohexane (passed through activated alumina). The reactor was heatedto 55° C. and 103.22 g of styrene (passed through activated alumina andQ5 catalyst bed) were added. The polymerization was initiated by adding7.8 mL of 1.32 M sec-butyl lithium solution. After stirring for 1 hour,1 mL of methanol was added to quench the polymerization. The solutionwas stirred for an additional 30 minutes as the reactor cooled. Thepolymer was isolated by precipitating it in 2 L of methanol and dryingit under vacuum at 90° C. overnight. A total of 101.96 g (99 percentyield) were collected. GPC analysis, versus narrow molecular weightpolystyrene standards, of the polymer gave M_(n)=8,296, M_(w)=8,679 andM_(w)/M_(n)=1.046. Other molecular weights of polystyrene were preparedanalogously.

Preparation of Hydroxy Terminated Anionically Polymerized Polystyrene

Charged to a 1 L one-neck round-bottom flask, equipped with magneticstirring bar, septum port with septum, and a nitrogen inlet adapter, was208 g of cyclohexane (passed through activated alumina) and 52.64 g ofstyrene (passed through activated alumina, distilled from calciumhydride and dibutyl magnesium). The polymerization was initiated at roomtemperature by adding 5.6 mL of 0.624 M sec-butyl lithium solutionresulting in an orange colored solution. After 2 hours, 2.31 g ofethylene oxide (dried over calcium hydride) were added to give acolorless solution. After 30 minutes, 2 mL of methanol (MeOH) were addedto terminate the polymerization. The polymer was isolated byprecipitating it in MeOH and drying under vacuum at 90° C. overnight.The yield was quantitative. GPC analysis, versus narrow molecular weightpolystyrene standards, gave M_(n)=14,960, M_(w)=16,035 andM_(w)/M_(n)=1.072. Other molecular weights of hydroxy terminatedpolystyrene were prepared analogously.

Preparation of a Star Polystyrene

To a 250 mL round bottom flask fitted with a Dean Starktrap/condenser/nitrogen inlet was added hydroxy terminated polystyrene(M_(n)=4837) (10.00 g, 0.0207 mole) and toluene (150 mL). The mixturewas stirred until the solid had dissolved. The mixture was heated toreflux for 2 hours to remove any water azeotropically. The solution wasallowed to cool to room temperature then the flask was sealed with arubber septum. Silicon tetrachloride (59 microliters, 0.000517 mole) wasadded via syringe and the mixture stirred for 5 minutes. Pyridine (50microliters) was added via syringe and the mixture stirred for 48 hoursat room temperature. The mixture was then heated to reflux for 1.5hours. The solvent was then removed in vacuo. The residue was dissolvedin methylene chloride, washed with HCl (aq.), and NaCl (sat.), thendried (MgSO₄) and solvent removed in vacuo. Analysis of the material bygel permeation chromatography indicated a M_(n)=16876 and a M_(w)=17222relative to polystyrene standards.

Formulation, Thin Film Formation, and Evaluation Using 8700 M_(n)Polystyrene

Anionically polymerized polystyrene with a M_(n) of 8700 was added, 20percent by mass relative to solids, to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 prepared as describedabove. The solution was optically transparent with a dark red castindicating dissolution of the polystyrene into the b-staged resin. Thesolution was applied to a silicon wafer and cast by spin-coating to forma 3.5 μm thick coating. The film was baked on an MTI hot plate at 320°C. for 2 minutes under nitrogen and then at 400° C. for 10 minutes undernitrogen. The coating on the wafer was further heated at 425° C. undernitrogen for 60 minutes in a Blue M oven. After this latter heatingstep, about 95 percent of the polystyrene was determined by fouriertransform infrared spectroscopy (FTIR) to have been removed. An estimateof the average pore size based on visual inspection of a TEM view of thefilm was about 300 nm. The index of refraction of the porous coating wasabout 1.5; this compares to an index of refraction of 1.63 for the fullydense matrix.

The solution containing polystyrene from above was applied to a siliconwafer and cast by spin-coating to form a 3.3 μm thick coating. The filmwas baked on a hot plate at 380° C. for 2 minutes under nitrogen andthen at 400° C. for 10 minutes under nitrogen. The coating on the waferwas then heated in an oven at 425° C. under nitrogen for 6 minutes. Thelatter heating step removed about 80 percent of the polystyrene asmeasured by FTIR. The estimated average pore size was 30 nm. Subsequentheating at 450° C. for 20 minutes removed most of the remainingpolystyrene. The pore morphology was essentially unchanged with anaverage pore size of 30 nm.

The solution containing polystyrene from above was applied to a siliconwafer and cast by spin-coating to form a 5.8 μm thick coating. The filmwas baked on an MTI hot plate at 340° C. for 2 minutes under nitrogenand then at 400° C. for 10 minutes under nitrogen. The coating on thewafer was further heated at 425° C. under nitrogen for 60 minutes in aBlue M oven. An estimate of the average pore size, based on visualinspection of a TEM view of the film, was about 300 nm.

Formulation, Thin Film Formation, and Evaluation Using 15,800 M_(n)Polystyrene

Anionically polymerized polystyrene with a M_(n) of 15,800, as purchasedfrom Scientific Polymer Products Inc., was added (20 percent by massrelative to solids) to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 prepared as describedabove. Mesitylene was added so that the total solids content was 20percent. The solution was applied to a silicon wafer and cast byspin-coating to form a 1.85 μm thick coating. The film was baked on ahot plate at 320° C. for 2 minutes under nitrogen and then at 400° C.for 10 minutes under nitrogen. The coating on the wafer was then heatedin an oven at 450° C. under nitrogen for 20 minutes. The estimatedaverage pore size was 200 nm. The volume fraction was measured to bebetween 11 percent and 15 percent using image analysis of the TEMmicrographs. The dielectric constant measured with a 0.25 inch diameterparallel plate capacitor was 2.3.

Formulation, Thin Film Formation, and Evaluation Using 12,400 MnPolystyrene

Anionically polymerized polystyrene with a M_(n) of 12,400 M_(n) aspurchased from Scientific Polymer Products Inc., was added (20 percentby mass relative to solids) to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 prepared as describedabove. The total solids content was adjusted to 15 percent withcyclohexanone. The solution was applied to four nearly identical 200 mmsilicon wafers and cast by spin-coating on a MTI 200 mm track coater toform a 0.9 μm thick coating. The films were baked on a hot plate on thetrack at 150° C. for 2 minutes under nitrogen. Subsequently, two of thefilms were baked at 320° C. under a 7 psi nitrogen purge on a hot platemodule contiguous to the track coater. The remaining wafers were bakedat 320° C. under a 55 psi nitrogen purge on a stand-alone module hotplate similar to the hot plate contiguous to the track. All four filmswere then baked at 400° C. for 10 minutes under the 55 psi nitrogenpurge and, finally, heated in an oven at 450° C. under nitrogen for 20minutes to remove the polystyrene. The wafers baked at 320° C. on the 7psi nitrogen purge hot plate suffered film loss proportional to theporagen content with the final thickness of 0.68 μm and refractive indexof 1.63; indicating film collapse in lieu of pore formation. The wafersbaked under the 55 psi purge had a final thickness of about 0.83 μm anda refractive index of 1.55; indicative of pore formation during the 450°C. heating step.

Formulation, Thin Film Formation, and Evaluation of Star Polystyrene inOligomer Solution from4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl Ether and1,3,5-Tris(phenylethynyl)benzene Mole Ratio 3:2

The star polystyrene material from above was added at a 20 weightpercent level, relative to solids, to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 described above. Thesolution was applied to a silicon wafer and cast by spin-coating to forma 2.2 μm thick coating. The film was baked on an MTI hot plate at 320°C. for 2 minutes under nitrogen and then at 400° C. for 10 minutes undernitrogen. The coating on the wafer was further heated at 425° C. undernitrogen for 60 minutes in a Blue M oven. An estimate of the averagepore size based on visual inspection of a TEM view of the film was about120 nm. The index of refraction of the porous coating was about 1.56.

EXAMPLE 5 Preparation of a Porous Polyarylene Thin Film Using a ReactivePolyamide Poragen

Preparation of Polyamide from Sebacoyl Dichloride and2,5-Dimethylpiperazine

To a 1 L round bottom flask was added 2,5-dimethylpiperazine(recrystallized from acetone) (10.0000 g, 0.08757 mole) and chloroform(400 mL). Triethylamine (23.1 mL, 0.1656 mole) was added via syringe.Sebacoyl chloride (19.799 g, 0.08279 mole) was weighed into a beaker,dissolved in chloroform (300 mL), and transferred to a dropping funnelattached to the 1 L round bottom flask. The solution of acid chloridewas added quickly to the solution of diamine. The dropping funnel wasrinsed with chloroform (50 mL) which was added to the reaction mixture.The mixture was stirred at room temperature for 10 minutes. The mixturewas then poured into hexanes (2 L) precipitating a white solid. Water (1L) was added and the mixture stirred. The liquid layer was decanted fromthe white solid. The solid was taken up in chloroform and the topaqueous layer was removed and discarded. Solvent was removed in vacuo.The residue was taken up in dimethylformamide and then precipitated intowater. The resultant solid was isolated by filtration and dried in vacuoat 100° C. overnight.

Reaction of Polyamide from Sebacoyl Dichloride and2,5-Dimethylpiperazine with 3,5-Bis(phenylethynyl)-benzoyl Chloride

3,5-Bis(phenylethynyl)benzoic acid (0.3224 g, 0.001 mole) was weighedinto a 25 mL round bottom flask. Thionyl chloride (10 mL) was added andthe mixture stirred for 2 hours at room temperature. The excess thionylchloride was removed by distillation then by application of vacuum. Theresultant solid was dissolved in chloroform and the solvent removed invacuo twice. The solid was then dissolved in chloroform. The polyamideprepared as described above (5.0 g, 0.0005 mole) was weighed into a 100mL round bottom flask and dissolved in chloroform (50 mL). The solutionof acid chloride was then added followed by triethylamine (0.5 mL). Themixture was stirred at room temperature for 17 hours. The reactionmixture was filtered through a 1 micron filter then diluted with hexanesprecipitating a light yellow solid. Solvent was decanted from the solidand additional hexanes were added. The solvent was again decanted offand the solid dried in vacuo at room temperature. A sample was analyzedby gel permeation chromatography which indicated a M_(n)=24100 and aM_(w)=43803.

Preparation of Oligomer Solution from4,4′-Bis(2,4,5-triphenyl-cyclopentadien-3-one)-diphenyl Ether,1,3,5-Tris(phenylethynyl)benzene and Polyamide Endcapped with3,5-Bis(phenylethynyl)benzamide Groups

To a 500 mL 3-necked round bottom flask was added4,4′-bis(2,4,5-triphenylcyclopentadienone)diphenyl ether (10.0000 g,0.01277 mole), 1,3,5-tris(phenylethynyl)benzene (4.8340 g, 0.01277mole), polyamide endcapped with 3,5-bis(phenylethynyl)benzamide groupsfrom above (3.7085 g, 0.000154 mole), and gamma-butyrolactone (43.27 g).The flask was attached to a nitrogen/vacuum inlet. The magneticallystirred solution was degassed by applying vacuum and refilling withnitrogen five times. The solution was then heated to an internaltemperature of 200° C. After 48 hours of heating, the solution wasallowed to cool to 145° C. then diluted with cyclohexanone (30.89 g).The solution was then allowed to cool to room temperature. Analysis ofthe final solution by gel permeation chromatography indicated aM_(n)=5071 and a M_(w)=14378 relative to a polystyrene standard. Thesolution was applied to a silicon wafer and cast by spin-coating to forma 1.5 μm thick coating. The film was baked on an MTI hot plate at 320°C. for 2 minutes under nitrogen and then at 400° C. for 10 minutes undernitrogen. The coating on the wafer was further heated at 450° C. undernitrogen for 20 minutes in a Blue M oven. The pore sizes based on visualinspection of a TEM view of the film appeared to be bimodal with largerpores of about 250 nm diameter and smaller pores of about 30 nm.

EXAMPLE 6 Preparation of a Porous Polyarylene Thin Film Using LatexParticles as Poragens

Formulation of Latex Particles in Oligomer Solution from4,4′-Bis(2,4,5-triphenylcyclo-pentadien-3-one)diphenyl Ether and1,3,5-Tris-(phenylethynyl)benzene Mole Ratio 3:2

Cross-linked latex solutions (such as those available from the DowChemical Company) were added at a 20 weight percent level, on a solidsto solids basis, to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 described above, whichhad been precipitated into water, dried, and redissolved in Dowanol PMAcetate. The solutions were heated to reflux in a round bottom flaskfitted with a Dean Stark trap/condenser/nitrogen inlet to remove thewater introduced with the latex particles by azeotropic distillation.The resultant solutions were cooled and then used in subsequentprocessing. A resin solution containing DW-110NA latex (from The DowChemical Company) as the poragen was prepared as described. The solutionwas applied to a silicon wafer and cast by spin-coating to form a 2.7 μmthick coating. The film was baked on an MTI hot plate at 320° C. for 2minutes under nitrogen and then at 400° C. for 10 minutes undernitrogen. The coating on the wafer was further heated at 450° C. undernitrogen for 20 minutes in a Blue M oven. The pores appeared to beoblate with the long axes in the plane of the film based on visualinspection of a TEM view of the film. The long axes were about 150 nmdiameter and short axis was about 50 nm.

EXAMPLE 7 Preparation of a Porous Polyarylene Thin Film Using aDendritic Polyester as Poragen Preparation of Boltron H40 Benzoate

Into a 250 mL round bottom flask equipped with a magnetic stirrer,equilibrating addition funnel, and a reflux condenser with a nitrogeninlet was added, with stirring, Boltron H40 dendritic polyester polymerhaving a theoretical molecular weight of 7,316 g permole (5.0 g, 8.75mmole OH per g, 44 mmole) and THF (70 mL). Pyridine (7 mL) was thenadded to the stirred solution. Benzoyl chloride (7.03 g, 50 mmol) wasadded dropwise to the solution over 15 minutes. Upon completion ofaddition, the reaction mixture was heated under reflux for 2 hours. Thereaction was then cooled to room temperature. The solution was filtered,diluted with 200 mL of methylene chloride, washed with 10 percent HCl(3×25 mL), then water (1×50 mL), then 1M NaOH (2×25 mL), then wateragain (1×50 mL), and then brine (1×50 mL). The organics were then driedover magnesium sulfate, and the solvent removed to yield the crudeproduct, which was further purified by precipitation into methanol toafford 7.4 g product (77 percent); the structure of which was confirmedby proton and carbon NMR spectroscopy.

Synthesis of 1,2,3,4-Tetrakis(phenylethynyl)benzene

In a 250 mL flask was placed 11.81 g (0.030 mole) of1,2,3,4-tetrabromobenzene (Collins, I., Suschitzky, H., J. Chem. Soc.,C, 1969, 2337), 27.0 g (0.267 mole) of triethylamine, 13.6 g (0.132mole) of phenylacetylene, and 60 mL of N,N-dimethyl formamide. Thereaction mixture was purged with nitrogen for 15 minutes and then 0.945g (0.0036 mole) of triphenylphosphine and 0.135 g (0.0006 mole) ofpalladium acetate were added. After heating the reaction mixture at 80°C. under nitrogen atmosphere for 20 hours, the flask was allowed to coolto room temperature, water (100 mL) and toluene (100 mL) were added. Theresulting organic layer was washed with 10 percent HCl, water andsaturated NaCl and dried with Na₂SO₄. The pure product (5.4 g, 38percent) was obtained upon removal of the solvent and recrystallizationfrom hexane/toluene mixture. ¹H NMR (CDCl₃, 300 MHz) δ 7.37 (m, 12H),7.50 (s, 2H), 7.62 (m, 8H) ¹³C NMR (CDCl₃, 75 MHz) δ 87.3, 88.1, 95.5,98.2, 123.1, 123.4, 125.7, 128.4, 128.5, 128.8, 130.9, 131.8, 131.9.

Formulation, Thin Film Formation, and Evaluation of Boltron H40Benzoate+1,2,3,4-Tetrakis(phenyl-ethynyl)benzene in Oligomer Solutionfrom 4,4′-Bis-(2,4,5-triphenylcyclopentadien-3-one)diphenyl Ether and1,3,5-Tris(phenylethynyl)benzene Mole Ratio 1:1

Boltron H40 Benzoate as prepared above, 25 percent by mass relative tosolids, and 1,2,3,4-tetrakis(phenylethynyl)benzene, 20 percent by massrelative to solids, were added to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 1:1 in gamma-butyrolactoneand cyclohexanone as described in WO 98/11149. The solution wasoptically transparent with a dark red cast indicating dissolution of theBoltron H₄₀ Benzoate and 1,2,3,4-tetrakis(phenylethynyl)benzene into theb-staged resin. The solution was applied to a silicon wafer and cast byspin-coating to form a 1.6 μm thick coating. The film was baked on anMTI hot plate at 320° C. for 2 minutes under nitrogen and then at 400°C. for 10 minutes under nitrogen. The coating on the wafer was furtherheated at 425° C. under nitrogen for 60 minutes in a Blue M oven. Anestimate of the average pore size based on visual inspection of a TEMview of the film was about 300 nm. Also, smaller pore structure wasapparent with sizes between 5 nm to 10 nm.

EXAMPLE 8 Preparation of a Porous Polyarylene Thin Film Using BlockCopolymers as Poragens

Preparation of Poly(styrene-block-methyl methacrylate) (PS-b-PMMA)

Charged to a 500 mL one-neck round bottom flask, equipped with magneticstirring bar, septum port with septum, and an addition funnel withseptum and nitrogen inlet, was 193 g of tetrahydrofuran (passed throughactivated alumina). The flask was cooled to −78° C. and 12.73 g ofstyrene (passed through activated alumina and Q5 catalyst bed) wereadded. The polymerization was initiated by adding 1.15 mL (0.84 mmole)of 0.733 M sec-butyl lithium solution resulting in an orange coloredsolution. After 2 hours, the poly(styrene) (PS) block was sampled byremoving an aliquot and adding it to methanol (MeOH), and 0.19 g (1.05mmoles, 1.25 equivalent) of diphenylethylene (distilled fromdiphenylhexyl lithium) were added to give a dark red color. After 25minutes, 13.18 g of methyl methacrylate (MMA) (distilled from calciumhydride and triethyl aluminum) were added dropwise via the additionfunnel over a 20 minute period. The red color dissipated after the firstseveral drops of MMA. After 1 hour, the polymerization was terminated byadding 0.2 mL of MeOH. The solution was allowed to warm to roomtemperature and the polymer was isolated by precipitating it in 600 mLof MeOH and collecting it by filtration. Both polymers were dried undervacuum at 60° C. for several hours. A total of 24.69 g (95 percentyield) of PS-b-PMMA were collected. GPC analysis, versus narrowmolecular weight polystyrene standards, of the PS block gaveM_(n)=14,567, M_(w)=15,821 and M_(w)/M_(n)=1.086; the PS-b-PMMAcopolymer gave M_(n)=26,825, M_(w)=28,893 and M_(w)/M_(n)=1.077. NMRanalysis of the block copolymer showed the PMMA block to haveM_(n)=15,364 giving M_(n)=29,913 for the copolymer.

Preparation of Poly(butadiene-block-ε-caprolactone) (PB-b-PCL)

Charged to a 1.5 L glass polymerization reactor, which had been cleanedwith refluxing toluene and dried under vacuum, was 650 mL of cyclohexane(passed through activated alumina). The reactor was heated to 50° C. and32.55 g of 1,3-butadiene (passed through activated alumina and Q5catalyst bed) were added. The polymerization was initiated by adding 7.0mL (9.1 mmoles) of 1.3 M sec-butyl lithium solution. After stirring for2.5 hours, the poly(butadiene) (PB) block was sampled, by removing analiquot and adding it to methanol (MeOH), and 1.58 g of (3.59 mmoles,3.9 eqivalent) of ethylene oxide (dried over calcium hydride) wereadded. The reactor temperature was increased to 70° C. After 20 minutes,9.1 mL (9.1 mmoles, 1.0 eqivalent) of 1.0 M diethylaluminum chloride and0.1 mL of tetrahydrofuran (passed through activated alumina) were addedto give a turbid solution. The reactor was cooled to 60° C. and 34.81 gof ε-caprolactone (distilled from calcium hydride twice) were added togive a milky solution. After 90 minutes, 0.5 mL of MeOH were added toterminate the polymerization. The solution was stirred for an additional30 minutes to assure complete termination and then was added to 0.75 gof 2,6-di-tert-butyl-4-methyl phenol. The polymer was isolated byprecipitating it in 1.2 L of methanol and drying it under vacuum at 50°C. for several hours. A total of 48.1 g (71 percent yield) of PB-b-PCLwere collected. GPC analysis, versus narrow molecular weightpoly(butadiene) standards, of the PB block gave M_(n)=4,890, M_(w)=5,080and M_(w)/M_(n)=1.039; the PB-b-PCL copolymer gave M_(n)=5,655,M_(w)=6,629 and M_(w)/M_(n)=1.172. NMR analysis of the block copolymershowed the PCL block to have M_(n)=4,794 giving M_(n)=9,685 for thecopolymer.

Formulation, Thin Film Formation, and Evaluation ofPoly(styrene-block-methyl methacrylate) (PS-b-PMMA) in Oligomer Solutionfrom 4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)-diphenyl Ether and1,3,5-Tris(phenylethynyl)benzene Mole Ratio 3:2

The block copolymer of polystyrene and PMMA as described above was added(20 percent by mass relative to solids) to the oligomer solution from4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 described above. Thesolution was optically transparent with a dark red cast indicatingdissolution of the block copolymer into the b-staged resin. The solutionwas applied to a silicon wafer and cast by spin-coating to form a 1.94μm thick coating. The film was baked on a MTI hot plate at 400° C. for10 minutes under nitrogen. The coating on the wafer was further heatedat 4500° C. under nitrogen for 20 minutes in a Blue M oven. An estimateof the average pore size based on visual inspection of a TEM view of thefilm was about 200 nm.

Formulation, Thin Film Formation, and Evaluation ofPoly(butadiene-block-b-caprolactone) (PB-b-PCL) in Oligomer Solutionfrom 4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl Ether and1,3,5-Tris(phenylethynyl)benzene Mole Ratio 3:2

The block copolymer of polystyrene and polycaprolactone described above(was added, 20 percent by mass relative to solids) to the oligomersolution from 4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenylether and 1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 describedabove. The solution was optically transparent with a dark red castindicating dissolution of the block copolymer into the b-staged resin.The solution was applied to a silicon wafer and cast by spin-coating toform a 2.85 μm thick coating. The film was baked on a MTI hot plate at320° C. for 2 minutes under nitrogen and then at 400° C. for 10 minutesunder nitrogen. The coating on the wafer was further heated at 450° C.under nitrogen for 20 minutes in a Blue M oven. An estimate of theaverage pore size based on visual inspection of a TEM view of the filmwas about 20 nm.

EXAMPLE 9 Preparation of a Porous Benzocyclobutene Film Using aFunctionalized Dendrimer as Poragen

A polyamidoamine dendrimer, generation 2, available from Dendritech,Inc., was functionalized with phenylpropiolic acid to afford a dendrimerwith 16 phenylpropiolamides at the periphery. The functionalizedpropiolamide (0.3 g) was added to 6.0 g of a solution of 25 weightpercent oligomeric divinylsiloxane-bis-benzocyclobutene inN-cyclohexylpyrrolidinone. The mixture was warmed to 60° C. and thencooled to room temperature and allowed to stand for 48 hours. The weightratio of dendrimer to benzocyclobutene oligomer was 16.7:83.3 and thetotal percent solids was 28.6 percent. The prepolymer solution wasfurther diluted with 2.7 g of N-cyclohexylpyrrolidinone to afford afinal solution of 20 weight percent solids. This solution was spun ontoa 4 inch silicon wafer (3 seconds per 500 rpm, then 30 seconds per 2000rpm) and then subjected to the following thermal treatment: 5 minutesper 200° C.; 6 minutes per 250° C.; hot plate 10 minutes per 350° C. andoven 9 hours per 300° C. The film was slightly hazy and when looked atby transmission electron microscopy (TEM) showed a distribution ofspherical, closed cell pores ranging in diameter from 5-200 nm.

EXAMPLE 10 Preparation of a Porous Polyarylene Thin Film Using aNon-reactive Star Polyethylene Glycol as Poragen Preparation of 8 ArmPoly(ethylene glycol) Benzoate

Into a 250 mL round bottom flask equipped with a magnetic stirrer,equilibrating addition funnel, and a reflux condenser with a nitrogeninlet was added, with stirring, branched PEG (8 arms, from ShearwaterPolymers) polymer having a molecular weight of 10,000 g per mole (5.0 g,4 mmole OH) and methylene chloride (40 mL). Triethylamine (5 mL) wasthen added to the stirred solution. Benzoyl chloride (1.69 g, 12 mmole)in 20 mL methylene chloride was added dropwise to the solution over 15minutes. Upon completion of addition, the reaction mixture was heatedunder reflux for 2 hours. The reaction was then cooled to roomtemperature. The solution was washed with 10 percent HCl (3×25 mL), thenwater (1×50 mL), then 1M NaOH (2×25 mL), then water again (1×50 mL),then brine (1×50 mL). The organics were then dried over magnesiumsulfate, and the solvent removed to yield the crude product, which wasfurther purified by precipitation into ether to afford 4.4 g of product(81 percent). The structure of which was confirmed by proton and carbonNMR spectroscopy.

Formulation, Thin Film Formation, and Evaluation of 8-Arm StarPoly(ethylene glycol) Benzoate in Oligomer Solution from4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl Ether and1,3,5-Tris(phenylethynyl) benzene Mole Ratio 3:2

The 8-arm star poly(ethylene glycol) benzoate described above, wasadded, 20 percent by mass relative to solids, to the oligomer solutionfrom 4,4′-bis(2,4,5-triphenylcyclopentadien-3-one)diphenyl ether and1,3,5-tris(phenylethynyl)benzene mole ratio 3:2 described above. Thesolution was optically transparent with a dark red cast indicatingdissolution of the poragen into the b-staged resin. The solution wasapplied to a silicon wafer and cast by spin-coating to form a 2.5 μmthick coating. The film was baked on a MTI hot plate at 400° C. for 2minutes under nitrogen and then coating on the wafer was further heatedat 450° C. under nitrogen for 20 minutes in a Blue M oven. An estimateof the average pore size based on visual inspection of a TEM view of thefilm was about 180 nm.

EXAMPLE 11 Preparation of a Porous Polyarylene Thin Film Using aPolystyrene-block-polyarylene

Preparation of Polystyrene Ester of 4-Phenylethynylbenzoic Acid

Into a 250 mL round bottom flask equipped with a magnetic stirrer, anequilibrating addition funnel, and a reflux condenser with a nitrogeninlet was added, with stirring, polystyrene, monohydroxyl terminatedpolystyrene (from Scientific Polymer Products) having a molecular weightof 10,000 g per mole (10.0 g, 1.0 mmole) and THF (50 mL). Pyridine (5mL) was then added to the stirred solution. 4-Phenylethynylbenzoylchloride (0.96 g, 4 mmol) in 10 ml THF was added dropwise to thesolution over 15 minutes. The reaction mixture was heated under refluxfor 2 hours and then cooled to room temperature. The solution wasfiltered, diluted with 200 mL of chloroform and washed with 10 percentHCl (25 mL), then water (50 mL), then 1M NaOH (25 mL), then water again(50 mL), and then brine (50 mL). The organics were then dried overmagnesium sulfate and the solvent removed to yield the crude product,which was further purified by precipitation into methanol to afford 9.3g of product.

Preparation and Thin Film Formulation and Evaluation of OligomerSolution from 4,4′-Bis(2,4,5-triphenylcyclopentadien-3-one)diphenylether, 1,3,5-Tris(phenylethynyl)benzene and Polystyrene Ester of4-Phenylethynylbenzoic Acid

To a 250 mL 3-necked round bottom flask was added4,4′-bis(2,4,5-triphenylcyclopentadienone)diphenyl ether (8.0 g, 0.0102mole), 1,3,5-tris(phenylethynyl)-benzene (3.71 g, 0.0098 mole),polystyrene ester of 4-phenylethynyl benzoic acid (M_(w)=10,000 g permole) (3.0 g, 20 percent relative to other solids), andgamma-butyrolactone (37.3 g). The flask was attached to anitrogen/vacuum inlet. The magnetically stirred solution was degassed byapplying vacuum and refilling with nitrogen five times. The solution wasthen heated to an internal temperature of 200° C. After 46 hours ofheating, the solution was allowed to cool to 145° C. then diluted withcyclohexanone (19.6 g). The solution was then allowed to cool to roomtemperature. The solution was applied to a silicon wafer and cast byspin-coating to form a 4.7 μm thick coating. The film was baked on a MTIhot plate at 320° C. for 2 minutes under nitrogen and then at 400° C.for 10 minutes under nitrogen. The coating on the wafer was furtherheated at 425° C. under nitrogen for 60 minutes in a Blue M oven. Anestimate of the average pore size based on visual inspection of a TEMview of the film was about 110 nm.

EXAMPLE 12 Preparation of a Porous Perfluorcyclobutane Thermoset ThinFilm Using a Gel-Swell-Cure Procedure

In this example, we used an oligomeric solution of perfluorcyclobuteneresin dissolved in mesitylene. The resin was spun coated onto 4 inchsilicon wafers at 3000 rpm's such that the thickness was near 1 micron.The resin was then reacted to past its gel point by placing the wafersin an oven which was idling at 161° C.; the oven ramped to 175° C. in 5minutes and then held at 175° C. for 46 minutes. After cooling to roomtemperature, the wafers were exposed to either no swelling solution; asolution of 90 percent mesitylene and 10 percent styryl-benzocyclobuteneby weight; or a solution of a solution of 90 percent mesitylene and 10percent styryl-benzocyclobutene by weight. The exposure was done bypuddling the solution onto the wafer for 1 minute in order to swell thenetwork. The wafer was then spun at 3000 rpms for 45 seconds to removeexcess solvent. After spinning, the wafer was placed onto a hot plateunder nitrogen purge for 1 minute at 325° C. to cure the film. Waferswere sampled at various points in the above process and the index ofrefraction was measured using ellipsometry at five different points andthen averaged. The results are listed in the table below. Table ofResults for Gel-Swell-Cure Experiments Swell Index of Wafer ProcessSequence Solution Refraction 1 Gel None 1.547 ± 0.009 2 Gel + Cure (noswell) None 1.521 ± 0.006 3 Gel + Swell + Cure 10% styryl-BCB 1.490 ±0.004 4 Gel + Swell + Cure 25% styryl-BCB 1.447 ± 0.019

14. A low dielectric constant material made by the method of claim 1having a dielectric constant less than 2.2.
 15. The material of claim 14wherein the average diameter of the pores is less than 20 nm.
 16. Anarticle comprising a substrate and the material of claim
 14. 17. Anintegrated circuit article comprising an active substrate containingtransistors and an electrical interconnect structure containingpatterned metal lines separated, at least partially, by layers orregions of a porous dielectric material, wherein the dielectric materialis a cross-linked hydrocarbon-containing matrix having a T_(g) ofgreater than 300° C.
 18. The article of claim 17 wherein thecross-linked resin is a cured product of cyclopentadienone and acetylenefunctional compounds.